Fuzzing provides a way to test for vulnerabilities through generating random data to push into an application. This can be used to test desktop applications, network applications, and just about anything else.
pfsense probably is the most well-known used used open-sourced Linux firewall appliance in used today. It provides an easy to use web page GUI and installation is extremely easy.
I spoke about using a tool such as Istio to secure and manage microservices. Istio released v1.0 on July 31, 2018 and currently is at v1.0.2 as of September 18, 2018.